Cellular silica product and method of fabrication



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' No Drawing.

Patented May i928. I

LUNITE-D STATES ,PATEN orrlca.

The present silica. product of low specificgravity which is of particular-value as a heat i sulator for refrigerators, furnaces or other tiermal devices.

When crystalline. temperature of about 1700 C. and then .is allowed tocool it is converted to a distinct allotropic crystalline form known ordinarily as beta cristoba-lite. 'Upon coolingmbelow about 230? C. the beta cristobalite comes cha nged to alpha. cristobalite which has a porous structure and is ance somewhat like loaf sugar.

When the same heatin and cooling steps are carried out with su cient' rapidlty another similar allotropic form of silica known as trid mite is formed which also is porous in i s Inaccordance with my invention cristo-' al state. Q

balite-ior-tridymite silica is further expanded by a gas to form a coherent body with innumerable microscopic cavities, number of larger cavities varying, in size up a bulk specific gravity of about 0.6 or lower .and a correspondingly low heat conductivity.

eiently high to volatilize the impregnant and F -soften the silica, thereby further expanding k as liquid orange shellac. The

the material in much the we the gases generated by yeast expand dough in the makin of bread. This second heating is carried out rapidly up to a temperature of about 17 C.

My invention may be further illustrated j by the following specifiexample'. Granu! lar quartz sand 1s heated to about 1700 (3.,

is held for about one-half hour at this -temperature, and then is cooled to-room temperature. The resulting loose. granular mass is either cristobalite or tridymitedepending on the rates of heating and cooling. This material is mixed-with theshellac solution quartz is heated to ainvention comprises av new frosty in appearand a smaller ,to about i g'in diameter. The product has or mum, nassacnusm'rs. nsemnon 'ro GENERAL ELECTRIC COMPANY, a co'nroaa'rrox or NEW 1031. 1

CELLULAR SILICA PRODUCT AND METHOD OF FABRICATION.

.. Afiplicatipn filed August is, 19%. aerial a. 213,195.

amount. of solution absorbed is regulated to introduce into the silica. shellac to the amount of about one per cent-by weight of the silica. The mixture is molded to desired shape and then is heated slowly to I about 400 0., the solventbeing first vaporized from the binder and the shellac residue thereupon being decomposed and carbonized.

The molded product next is heated rapidly to a temperature of about 1750 C. to eliminate the binder residue and to soften the silica and seal over its exterior surface.

The binder leaves very'little or no carbon residue and produces the multiplicity 01 small cavities or blebs. These blebs are not connected with oneanother and hence the material is impervious to moisture.- The heat conductivity of the intumescent sllica' product is so low that when an oxyhydrogen flame is played upon a slab thick practicall no sensatio'n of heatcan be felt by the ban upon the o posite side.

What I claim asnew an desire to secure? by Letters Patent of the United States is 1. A silicaproductwhich issubstantially impervious-to moisture and is filled with fine cavities of such number that the specific gravity of than unity.

2. The method of treating silica; consists in converting'the' same to us condition, impregnating the silica in this condition with an organic binder and there- :perature below about 230 (3., im

silica having a specific gravity 0 {my hand this eleventh dag of Au upon heating to a fusion temperature. w

' 3. The method of preparing highly porous silica which consists in heating. crystalline silica toabout-1700 (3., cooling-to a temregna'ting with a decomposable binder an reheating rapidly to about 1750 C.

4. A heat insulator comprising a mass of about .6, a low heat conductivity, being substantially moisture" impervious and containin many 3 unconnected cavities varyin from a 1111 inch down to microscopic mansions.

In witness whereof, I' have hereunto set.

. at 1997? HAROL 

